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31.
[reaction: see text] trans-(3S)-Amino piperidines bearing various alkyl and aryl substituents at the C-4 position were synthesized via a ring-closing metathesis reaction. The absolute stereochemistry was controlled using a protected D-serine as a starting material. Stereoselective hydrogenation of allylamines provided trans-(3S)-amino-(4R)-alkyl- and -(4S)-aryl-piperidines. This procedure presents the first method for the asymmetric synthesis of 4-substituted 3-amino piperidines. 相似文献
32.
Mathew A. Cleveland Nick A. Gentile Todd S. Palmer 《Journal of computational physics》2010,229(16):5707-5723
Implicit Monte Carlo (IMC) and Implicit Monte Carlo Diffusion (IMD) are approaches to the numerical solution of the equations of radiative transfer. IMD was previously derived and numerically tested on grey, or frequency-integrated problems [1]. In this research, we extend Implicit Monte Carlo Diffusion (IMD) to account for frequency dependence, and we implement the difference formulation [2] as a source manipulation variance reduction technique. We derive the relevant probability distributions and present the frequency dependent IMD algorithm, with and without the difference formulation. The IMD code with and without the difference formulation was tested using both grey and frequency dependent benchmark problems. The Su and Olson semi-analytic Marshak wave benchmark was used to demonstrate the validity of the code for grey problems [3]. The Su and Olson semi-analytic picket fence benchmark was used for the frequency dependent problems [4]. The frequency dependent IMD algorithm reproduces the results of both Su and Olson benchmark problems. Frequency group refinement studies indicate that the computational cost of refining the group structure is likely less than that of group refinement in deterministic solutions of the radiation diffusion methods. Our results show that applying the difference formulation to the IMD algorithm can result in an overall increase in the figure of merit for frequency dependent problems. However, the creation of negatively weighted particles from the difference formulation can cause significant numerical instabilities in regions of the problem with sharp spatial gradients in the solution. An adaptive implementation of the difference formulation may be necessary to focus its use in regions that are at or near thermal equilibrium. 相似文献
33.
Laser-induced acoustic wave generation/propagation/interaction in water in various internal channels
Seung Hwan Ko Daeho Lee Heng Pan Sang-Gil Ryu Costas P. Grigoropoulos Nick Kladias Elias Panides Gerald A. Domoto 《Applied Physics A: Materials Science & Processing》2010,100(2):391-400
Short pulsed laser-induced single acoustic wave generation, propagation, interaction within a water-filled internal channel
are experimentally and numerically studied. A large-area, short-duration, single-plane acoustic wave was generated by the
thermoelastic interaction of a homogenized nanosecond pulsed laser beam with a liquid–solid interface and propagated at the
speed of sound in water. Laser flash Schlieren photography was used to visualize the transient interaction of the plane acoustic
wave in various internal channel structures ((a) sudden expansion and contraction channels, (b) bifurcating channels, (c) gradual
contraction wall channels and (d) a cylinder). Fairly good agreement between the experimental results and numerical simulation
is observed. 相似文献
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36.
Radiolysis of Aqueous Solutions of Benzoate Ion: A Radiation Chemistry Experiment for Undergraduates
This investigation describes the chemical effects of ionizing radiation on dilute aqueous solutions of benzoate ion. We have composed an experimental procedure that allows undergraduate chemistry students to identify and to quantitatively determine the amount of the products that are produced. The student investigators determine the absorbed dose that a sample receives when exposed to a 60Co source, irradiate dilute aqueous solutions of benzoate ion, and analyze the resulting mixture of hydroxybenzoate ions using high-performance liquid chromatography. The radiolysis of dilute solutions of benzoate ion results in the formation of a mixture of ortho-, meta-, and para-hydroxybenzoate ions that are readily separated on a C18 -Bondapak column. By the use of appropriate calibration curves, the yield (G values) of each of the isomers may be determined and compared.This paper was presented at the 15th Biennial Conference on Chemical Education, Waterloo, Ontario, Canada, August 1998 by N. Zevos and at the 26th Northeast Regional Meeting of the American Chemical Society by Evon Powell. 相似文献
37.
Wojciech Czardybon Wojciech Sokol John Warkentin Nick Henry Werstiuk 《Journal of Physical Organic Chemistry》2008,21(1):41-46
Synthesis of a bicyclic 2,2‐dioxa oxadiazoline (6,7‐diaza‐1‐methoxy‐5‐methyl‐2,8‐dioxabicyclo[3.2.1]oct‐6‐ene) is reported. Its thermolysis at 27°C is about 200 times as fast as the thermolysis of a monocyclic oxadiazoline model system. Presumably, a cyclic dioxa carbonyl ylide is formed initially and the ylide then undergoes a bond scission to afford either a dioxacarbene or a dialkylcarbene or it cyclizes to an oxirane. A small fraction of a dialkylcarbene was trapped as the product of addition to dimethyl acetylenedicarboxylate (DMAD). Computations of the barriers to the loss of N2 from the oxadiazolines and to the formation of the carbenes from the carbonyl ylide resulting from thermolysis of the bicyclic oxadiazoline are compared to corresponding barriers for a similar monocyclic oxadiazoline. The rate acceleration is accounted for in terms of geometric factors. The complex products from the decomposition of the bicyclic oxadiazoline were not studied. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
38.
We present a new method to measure the polarization state of a terahertz pulse by using a modified electro-optic sampling setup. To illustrate the power of this method, we show two examples in which the knowledge of the polarization of the terahertz pulse is essential for interpreting the results: spectroscopy measurements on polystyrene foam and terahertz images of a plastic coin. Both measurements show a sample-induced rotation of the terahertz electric field vector, which is surprisingly large and is a strong function of frequency. A promising aspect of our setup is the possibility of simultaneously measuring both transversal electric field components. 相似文献
39.
Tran NE Lambrakos SG Moore PG Ashraf Imam M Dulcey CS 《The Journal of chemical physics》2004,120(21):10257-10262
A prototype case study is presented that examines the level of hydrogen content in H-SWNTs using the Surface Plasmon Resonance technique. The damping effect and the angular shift in the resonance minimum of an SWNT-gold interface due to the presence of hydrogen is analyzed using a parametric model, which is based on the concept of an effective permittivity. The new approach provides for a non-invasive analysis of the level of hydrogen content in H-SWNTs and is potentially extendable to other carbon-based hydrogen storage materials. 相似文献
40.
Markowicz PP Tiryaki H Pudavar H Prasad PN Lepeshkin NN Boyd RW 《Physical review letters》2004,92(8):083903
We have observed a dramatic enhancement of third-harmonic generation in 3D polystyrene-air photonic crystals pumped by a near infrared laser beam. As the pump wavelength is tuned, the peak of the enhancement occurs when the third-harmonic wavelength approaches the short-wavelength edge of the band gap. We show that the origin of the enhancement is phase matching provided by the periodic structure of the photonic crystals. 相似文献